The recent USN-48-1 fixed a buffer overflow in xpdf. Since CUPS
contains xpdf code to convert incoming PDF files to the PostScript
format, this vulnerability applies to cups as well.

In this case it could even lead to privilege escalation: if an
attacker submitted a malicious PDF file for printing, he could be
able to execute arbitrary commands with the privileges of the
CUPS server.

Please note that the Ubuntu version of CUPS runs as a minimally
privileged user 'cupsys' by default, so there is no possibility of
root privilege escalation. The privileges of the 'cupsys' user are
confined to modifying printer configurations, altering print jobs,
and controlling printers.

Ariel Berkman discovered a buffer overflow in the ParseCommand()
function of the HPGL input driver. If an attacker printed a
malicious HPGL file, they could exploit this to execute arbitrary
commands with the privileges of the CUPS server.

Bartlomiej Sieka discovered three flaws in lppasswd. These allowed
users to corrupt the new password file by filling up the disk,
sending certain signals, or closing the standard output and/or error
streams.